Hollow screw rotary heat exchanger



Se t. 4, 1956 c R|ETZ 2,761,657

HOLLOW SCREW ROTARY HEAT EXCHANGER Original Filed Oct. 22, 1946 2 mshee 1 FIEJ L INVENTOR. G'Br/ A Riel;

ATTORNEY Sept. 4, 1956 c. A. RIETZ HOLLOW SCREW ROTARY HEAT EXCHANGER Original Filed 001, 22, 1946 2 Sheets-Sheet 2 INVENTUR. C'ar/ /7. Q3); m

ITTORNEY United States Patent HOLLOW SCREW ROTARY HEAT EXCHANGER Carl A. Rietz, San Francisco, Calif., assignor to Rietz Manufacturing Co., San Francisco, Calif., a corporatron of California Original application October 22, 1946, Serial No. 704,891, new Patent No. 2,610,033, dated September 9, 1952. Divided and this application April 1, 1952, Serial No. 280,995

2 Claims. (Cl. 257--79) This invention relates generally to material handling and treatment apparatus, particularly apparatus of the type making use of heat transfer screws having helicoidal flights for engaging the material. The present applicatron is a division of my copending application 704,891, filed October 22, 1946, now Patent No. 2,610,033 dated September 9, 1952.

It is an object of the invention to provide apparatus of the above character having a heat transfer screw particularly effective in promoting intermixing of the material being treated.

A further object of the invention is to provide an improved form of cooker for the treatment of various pulps or slurries, and which is characterized by efficient and rapid transfer of heat to the material being treated Without injury to the same.

Another object of the invention is to provide novel methods for the treatment of material by use of the foregoing apparatus, and applicable particularly where it is desired to secure an efficient exchange of heat with respect to the material.

Additional objects of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawing.

Referring to the drawing:

Figure l is a side elevational view illustrating one embodiment of the invention.

Figure 2 is a detail showing a portion of the heat transfer screw.

Figure 3 is an enlarged cross-sectional detail showing the construction of the screw flight.

Figure 4 is a detail showing an extended length of the screw and its mixing ribbon.

Figure 5 is a cross-sectional view taken laterally through Figure 4.

Figure 6 is a side elevation in section showing apparatus in which two screws are employed.

Figure 7 is a cross-sectional view taken along the line 7-7 of Figure 6.

That form of the invention illustrated in Figures 1 to 3 inclusive comprises an enclosing housing 10 provided with a feed hopper 11 and a discharge conduit 12. Extending longitudinally within this housing there is a screw 13 adapted to be rotated from some suitable source of power.

The screw is formed to receive heat transfer fluid, and

utilizes the novel construction illustrated in Figures 1 to 3, and claimed in my said application 704,891. Thus the screw includes the tubular shaft 14 which carries a helicoidally formed flight structure designated generally at 16. The flight structure is of fabricated construction and includes the metal walls 17, 18 and 19. Wall 17 is disposed helicoidally about the shaft and has its inner edge attached to the same by welding 21. Wall 18 is preferably of lesser width than wall 17 and is disposed in spaced substantially parallel relationship thereto. The inner edge of wall 18 is likewise attached to the shaft 14 by welding 22.

Wall 19 is attached to the walls 17 and 18 substantially as illustrated in Figure 3. Thus as illustrated its one edge abuts the rear side of wall 17 and is attached thereto by welding 23, and its other edge caps the outer periphery of wall 18 and is attached thereto by weld connection 24.

In operation the screw is rotated in such a direction that the outer or exposed face of wall 17 contacts and applies thrust to the material being handled. It will be noted that weld connection 23 lies completely behind the exposed face of wall 17, and therefore it is protected against abrasion and wear. The space 26 within the flight is adapted to receive a heat transfer fluid, and is in free communication at a number of points with the interior of the shaft 14, as for example by means of one or more slots 27 and openings 28. Where the screw is being constructed in such a manner as to withstand considerable internal pressure, it is desirable to attach walls 17 and 18 together at spaced points by means of the stay bolts or rivets 29.

At one end of the housing a suitable stuffing box or gland 31 is provided, by means of which steam or like heat transfer fluid supplied by way of pipe 32 is introduced into the passage through shaft 14, and thus into the flight. At the other end of the housing a similar gland 33 is provided by means of which condensate is removed through pipe 34.

It will be evident that the apparatus described above can be used for a variety of material handling and treating operations. Assuming that it is desired to heat pulps or slurries such as are frequently found in the food industry, as for example soup or meat stocks, steam at a suitable pressure and temperature is continuously supplied to the screw by way of pipe 32, and the material to be treated is supplied through hopper 11 either continuously or intermittently. Rotation of the screw is in such a direction that there is a progression of the material toward the outlet end of the housing. The exposed face of the wall 17 is the only surface of the flight which directly contacts and presses against the material being handled, and therefore the weld connections 23 and 24 are not weakened by abrasion. The fabricated flight construction provides a relatively high degree of strength to apply the desired thrust to the material and also to withstand internal pressure which may be applied. There is relatively good heat transfer from the steam introduced into the flight and the material being treated, whereby the material can be heated to any desired temperature before its discharge.

As shown in Figures 4 and 5, the feed screw is provided with one or more so-called mixing ribbons 36. In this instance two such ribbons are provided and they are disposed apart. Each ribbon consists of a strap of metal formed helicoidally and having its inner edge attached at spaced points to the periphery of the flight 16. It will be noted that the pitch of each of the ribbons is the same, and that this pitch is substantially greater than the pitch of the flight 16. In Figure 4 the helicoids of the flight and of the mixing ribbons are in opposite directions, although as will be presently explained in some instances it is desirable that they be in the same direction. The ends of the ribbons are preferably provded with inwardly extending vanes or paddles 37 With use of the screw illustrated in Figure 4 in a housing and associated parts substantially as illustrated in Figure l, the mixing ribbons impart considerable turbulence to the material being treated as the screw rotates. Such turbulence materially aids in intermixing the material being treated, and in insuring relatively high heat transfer through the walls of the flight. This is by virtue of the fact that turbulence extends into the regions between convolutions of the flight, thus enabling a relatively high rate of heat transfer without undue localized heating of the material being treated. The vanes or paddles 37 sweep the ends of the housing, thus tending to prevent formation of pockets where material may remain without entering into progressive treatment.

Figures 6 and 7 illustrate an equipment incorporating the present invention and particularly adapted for the heat treatment of various pulps or slurries, as for example the pasturization or cooking of food slurries like meat stocks. The apparatus consists of a suitable housing 41 carried by the end standards 42, and within which are disposed the two screws 43a, 43b. These screws can be constructed substantially like the screw of Figure 4, although it is desirable that the helix of the flight and of the mixing ribbons be in the same direction. The walls of the housing 41 include the substantially semi-cylindrical wall portions 44 which underlie the screws, and which join along the central longitudinal rib 46. The walls are provided with a suitable jacket 47 whereby heat transfer fluid such as steam may be applied to the outer walls of the housing. Connections can be made to this jacket by pipes 48. Centrally of the housing there is a valve controlled pipe 49 through which the treated material can be discharged. By suitable means such as gearing 51 the shafts of the two screws are interconnected for synchronous rotation in opposite directions. Packing glands 52 and 53 are provided at the ends of the housing and connect with pipes 54 and 55, for introduction of steam and removal of condensate.

To utilize the apparatus of Figure 6 a quantity of material to be treated, such as soup or meat stock, is introduced into the housing with the two screws being driven in opposite directions. Steam is supplied to both of the screws whereby heat transfer occurs to the material being handled through the walls of the flights. At the same time steam or like heating fluid can be applied to the outer jacket 47. The screws are completely or substantially submerged by the batch of pulp being treated, and as the screws rotate the flights tend to urge the material in their vicinities longitudinally of the housing and in opposite directions toward the ends of the same. At the same time the mixing ribbons cause general turbulence and intermixing of the material to promote heat transfer as previously described. At the ends of the housing there is a general crossing over of the material, or in other words there is a general transfer of the material from the region of one screw to the other. Thus during its treatment within the housing the material generally progresses longitudinally of the housing in opposite directions in the regions of the two screws, with a cross over at the ends of the housing, and at the same time there is a sidewise turbulent action or sidewise regurgitation caused by the mixing ribbons.

I claim:

1. A screw construction adapted to effect movement of material in a housing and to effect a heat transfer relative to the material, comprising a tubular shaft, a helicoidal flight forming a continuous thrust wall attached to the shaft and serving to cause movement of the material longitudinally of the housing upon rotation of said shaft, said flight being hollow and extending with a uniform radial width about said shaft, the interior of said flight being in communication with the interior of said tubular shaft to thereby receive heat transfer fluid, and a plurality of circumferentially spaced mixing ribbons attached at spaced points along the length of the same to the outer peripheral edge of the flight, said mixing ribbons being formed helicoidally and in an opposite direction to that of the flight but with a pitch substantially greater than the pitch of the flight, the portions of said ribbons between said points of attachment extending between adjacent convolutions of the helicoidal flight, said ribbons upon rotation of said shaft serving to form a zone of agitation and intermixing in a region adajacent the outer periphery of the flight.

2. Material handling apparatus of the character described comprising a housing and a pair of horizontal screws disposed within the housing in side by side parallel relationship, each of said feed screws comprising a tubular shaft, a helicoidal flight forming a continuous thrust wall attached to the shaft and serving to cause movement of material longitudinally of the housing upon rotation of said shaft, said flight being hollow and extending with a uniform radial width about said tubular shaft, the interior of said flight being in communication with the interior of the tubular shaft to thereby receive heat transfer fluid, and a pair of circumferentially spaced mixing ribbons attached at spaced points along the length of the same to the outer peripheral edge of the flight, said mixing ribbons being formed helicoidally in an opposite direction from the flight but with a pitch substantially greater than the pitch of the flight, the portions of said ribbons between said points of attachment extending between adjacent convolutions of the helicoidal flight, a pair of paddles mounted on said tubular shaft adjacent the ends of the housing and having their outer ends connected to said mixing ribbons, said pair of screws upon rotation serving to cause movement of material in opposite directions longitudinally of the housing and said paddles serving to sweep the ends of the housing and cause a transfer of material from one flight to another.

References Cited in the file of this patent UNITED STATES PATENTS 319,311 Peters June 2, 1885 1,420,008 Wilkel et a1 June 20, 1922 1,457,325 Thatcher June 5, 1923 2,027,185 Loomis Jan. 7, 1936 2,135,325 Burt et a1 Nov. 1, 1938 2,153,082 Grill et al. Apr. 4, 1939 2,321,185 Christian June 8, 1943 

